The major emphasis will be the continuation of ongoing studies to characterize the discriminative stimulus properties of narcotic agonists and antagonists in the rat and squirrel monkey. The governing hypothesis is that the components of action of narcotic agonists and antagonists that enable them to function as discriminative stimuli in animals are analogous to the components of action that engender subjective effects in man. Thus, discrimination paradigms could provide animal models for the preclinical identification and evaluation of the components of action of opioids that underlie their abuse potential. Independent groups of rats and squirrel monkeys will be trained to discriminate between saline and either morphine or cyclazocine. Stimulus generalization curves for novel drugs will be determined in each group and interspecies comparisons of the stimulus properties of compounds in animals trained with the same drug as well as intraspecies comparisons in animals trained with different drugs will be made. Stimulus generalization gradients in the rat will also be assessed as a function of training dose. Finally, discriminative stimuli associated with the morphine withdrawal syndrome will be characterized in morphine-dependent rats trained to discriminate between injections of saline and the narcotic antagonist naltrexone.